This chapter outlines recent progress in the study of the Vibrio genomes, including information from the genome sequences covered to date. A Japanese group and an American group independently reported the possession of two circular chromosomes for vibrios. First, all the vibrios examined possessed two chromosomes: no vibrios with only one chromosome were found. Second, the size of the large chromosome was relatively constant among the vibrios. The distribution of genes of known function between the large and small chromosomes of vibrios provides tantalizing clues about how the two-chromosome configuration of the Vibrionaceae might confer an evolutionary advantage. Thus, whatever the origin of the small chromosome of vibrios, stable maintenance of genomes with multiple chromosomes might have required the evolution of shared mechanisms to control replication. Genome sequencing of three Vibrio species enabled the authors to precisely compare the genome structures of the strains. The chapter provides a brief introduction to some recent topics on horizontal gene transfer in vibrios, mainly in relation to the acquisition of the genes for pathogenicity. Recently, it was reported that chromosomal superintegrons of vibrios might be a genetic source for the evolution of resistance to clinically relevant antibiotics through integron-mediated recombination events. As with Vibrio parahaemolyticus, further genome sequencing and comparative analysis of more vibrios should give us exciting new knowledge about vibrios exhibiting a variety of lifestyles.

Comparison of the size of the large and small chromosomes. The vertical axis is the relative size of each chromosome from various vibrios; the chromosomes of V. parahaemolyticus were used as a standard. The size differences of the chromosomes of each vibrio are presented by dividing the size of the large or small chromosome of each strain by the size of the corresponding chromosome of V. parahaemolyticus. Black bars, large chromosomes; gray bars, small chromosomes.

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FIGURE 2

Comparison of the size of the large and small chromosomes. The vertical axis is the relative size of each chromosome from various vibrios; the chromosomes of V. parahaemolyticus were used as a standard. The size differences of the chromosomes of each vibrio are presented by dividing the size of the large or small chromosome of each strain by the size of the corresponding chromosome of V. parahaemolyticus. Black bars, large chromosomes; gray bars, small chromosomes.